1. Field of the Invention
The present invention relates to a display unit containing a display driver IC (integrated circuit) and an MPU controlling the display driver IC, an electronic device using the display unit, and a method of inspecting the display unit.
2. Description of the Related Art
FIG. 1 is a schematic sectional view of a display unit of a cellular phone. As shown in FIG. 1, the display unit of a cellular phone comprises a liquid crystal module 20 using a liquid crystal display driver IC 10 with an inspection circuit built therein, a printed circuit board 30 with an MPU 300 mounted thereon, and a connector 40 electrically connecting the liquid crystal module 20 and the printed circuit board 30. The connector 40 is made of an elastic connecting member (zebra rubber) having conductive parts and insulating parts alternately formed, for example. The elastic connecting member 40 is formed from conductive parts and insulating parts alternately layered in the longitudinal direction from the back side to front side of the drawing in FIG. 1. The terminals of the liquid crystal module 20 and the terminals of the printed circuit board 30 are electrically connected by evenly applying a pressure to the elastic connecting member 40 in the longitudinal direction.
The liquid crystal module 20 has a liquid crystal display section 28 having a structure in which a liquid crystal 26 is sealed between two glass substrates 22 and 24. The liquid crystal display driver IC 10 is mounted on the extended portion of the substrate 24.
Here, if the pressure applied to the elastic connecting member 40 is not even, the connection of the liquid crystal module 20 and the printed circuit board 30 becomes faulty.
Inspection of the connection has conventionally been performed by driving the liquid crystal display driver IC 10 based on a signal from the MPU 300 for displaying the display patterns on the liquid crystal display section 28 and visually inspecting the patterns.
The manufacturing process of this type of display unit has been completely automated except the above-described visual inspection process. only the inspection process cannot be automated because it requires the visual inspection.
Moreover, because a faulty connection may be overlooked by mistake in the visual inspection, such inspection must be improved in terms of accuracy.
Furthermore, marketing strategy of electronic equipment manufacturers to satisfy recent demands of end users requires fabrication of several types of display units each having different specifications such as a display capacity, screen size, and other items. In this case, if the parts having different specifications are separately fabricated, not only an increased number of parts to be fabricated results in an increase in the cost, but also handling of the parts becomes complicated.
An object of the present invention is therefore to provide a display unit in which faulty connections of the connector can be automatically inspected, an electronic device using such a display unit, and a method of inspecting the display unit.
Another object of the present invention is to provide a display unit which can inspect abnormalities in the output of the booster circuit or the output of the oscillation circuit in the inspection process for faulty connections of the connector or which can read the ID of the display driver IC, an electronic device using such a display unit, and a method of inspecting the display unit.
Further object of the present invention is to provide a display unit in which the MPU can be used in common to a plurality of types of display driver ICs and can correctly set a controlling content for the display driver ICs built therein, an electronic device using such a display unit, and a method of inspecting the display unit.
A display unit of one aspect of the present invention comprises: a display section; a display driver IC driving the display section; a first board on which the display driver IC is mounted; an MPU sending a command and display data to the display driver IC; a second board on which the MPU is mounted; and a connector electrically connecting the first and second boards to each other, and further incorporates a device for inspecting the connection of the connector for faulty connection.
In the display unit of this aspect of the present invention, the MPU has a circuit for sending a test command during inspection mode, and reading an inspection result signal output thereafter from the display driver IC, and the display driver IC includes: an interface circuit for outputting and inputting a signal to and from the MPU; a command decoder for decoding the test command input from the MPU via the interface circuit; and an inspection circuit for outputting the inspection result signal in accordance with the signal from the command decoder.
In the display unit of this aspect of the present invention and a method of inspecting the display unit, the MPU reads the inspection result signal input via the interface circuit and the connector so that a faulty connection of the connector is judged.
Specifically, when the inspection result signal is normal, the connection by the connector on the output paths of the inspection result signal can be judged to be normal. Since the condition of connection by the connector can be inspected in this manner without relying on visual inspection, the inspection process can be automated.
In this aspect of the present invention, the first board may be a glass plate and the display section may be a liquid crystal display section including the glass plate.
When the first board is a glass plate which is part of the liquid crystal display section, various circuits (including the MPU) other than the display driver IC driving the liquid crystal display section may be formed on the second board which is connected to the display driver IC via the connector.
In this aspect of the present invention, the display driver IC may comprise: a storage section to which display data input from the MPU via the interface circuit is written; a display driver driving the display section based on the display data written in the storage section; and a booster circuit that generates voltages to be supplied to the display driver by boosting voltage.
Here, the booster circuit may be connected with at least one booster capacitor through the connector.
On the other hand, the inspection circuit may comprise; a comparator comparing an output of the booster circuit with a reference value; and a latch circuit latching a fail status at a time when the output of the booster circuit falls below the reference value, according to a result of comparison by the comparator.
In the display unit of this configuration, the MPU may send a test command for monitoring an output voltage of the booster circuit driven by a booster clock in the inspection mode, and then may read the inspection result signal after waiting for at least one period of the booster clock.
The fail state is thereby latched by the latch circuit when at least one booster capacitor is not normally connected to the booster circuit due to faulty connection. In this abnormal situation, the above-described fail state occurs without fail during one period of booster clock. Therefore, the faulty connection can be detected when the MPU reads the inspection result signal after one period of booster clock or a longer time.
In this aspect of the present invention, the display driver IC may have an ID setting circuit incorporated therein.
In this case, the MPU may send a test command for monitoring an output of the ID setting circuit during the inspection mode. The inspection circuit may output the inspection result signal according to the outputs of the ID setting circuit after the test command is decoded by the command decoder. It is also possible for the MPU to judge whether the connection condition of the connector is normal or abnormal by reading the inspection result signal as the ID information.
It is more preferable that the inspection circuit outputs the inspection result signal including high significant bits and low significant bits based on the output of the ID setting circuit, and the high significant bits and the low significant bits are brought into a relationship of non-inverted and inverted based on a signal produced by decoding the test command by means of the command decoder.
In this case, the MPU can decide the connection condition of the connector by judging whether the high significant bits and the low significant bits of the inspection result signal are in a relationship of non-inverted and inverted.
In this aspect of the present invention, the display driver IC may have an oscillation circuit that oscillates based on the logic power supply voltage supplied via the connector; and the interface circuit may have a data input-output terminal, a serial clock terminal, and an autoreturn circuit that switches the data input-output terminal between an input-allowable state and an output-allowable state every time a predetermined number of serial clock pluses supplied from the MPU via the serial clock terminal is counted.
In this case, the MPU may send the test command for monitoring an output of the oscillation circuit and the predetermined number of serial clock pluses in the inspection mode, may stop sending the serial clock pluses when inputting the output from the oscillation circuit via the inspection circuit and the data input-output terminal, and may send the predetermined number of serial clock pluses after reading the output of the oscillation circuit. On the other hand, the display driver IC may set the data input-output terminal in the input-allowable state according to an operation of the autoreturn circuit that counts the serial clock pluses input after sending the output of the oscillation circuit.
Usually the frequency of the output of the oscillation circuit is sufficiently lower than the frequency of the serial clock, so that the output of the oscillation circuit may not change at all when the output of the oscillation circuit is monitored according to the serial clock. For this reason, the serial clock is stopped while the output of the oscillation circuit is being monitored. After reading the output of the oscillation circuit, the MPU sends a predetermined number of serial clock pulses so that the input-output terminal can be switched to the input-allowable state.
A display unit of another aspect of the present invention comprises: a display section; a display driver IC driving and controlling the display section; and an MPU sending a command and display data to the display driver IC, and the display driver IC comprises: an ID setting circuit; and a command decoder decoding the command from the MPU, the MPU has a storage section for storing a plurality of types of control contents for a plurality of types of display driver ICs including the display driver IC, the MPU sends an ID monitor command to the display driver IC when the MPU reads an ID from the ID setting circuit, the display driver IC sends ID information from the ID setting circuit to the MPU in accordance with a signal generated by the command decoder decoding the ID monitor command, and the MPU reads the ID information and so as to control the display driver IC according to the corresponding control contents in the storage section.
This configuration not only enables the MPU to be used commonly by a plurality of types of display driver ICs, but also ensures the control contents for the display driver IC connected to the MPU to be selected according to the ID information read out from the display driver IC.
An electronic device of further aspect of the present invention comprises the display unit described above so that display malfunction may be reduced.